Indirectly heated cathode for valves operating on decimetric waves



Aug. 8, 1950 P. CAHOUR ETA INDIRECTLY HEATED CATHODE FOR VALVESOPERATING on DECIMETRIC WAVES Filed on. 22, 1947 N N W L s w s QM! N JK: M I I mu 1% 1' Q m; R

- INVENTOR. Pierre (a/war el al Patented Aug. 8, 1950 VALVES OPERATING NWAVES DECIMETRIG Pierre (labour and Andre J". Velte', Paris, France,assignors to Compagnie' Gcnerale De Tele graphic Sans Fil, a corporationof France Application October 22, 1947, Sam No. 781,432

' In France O'ctoberd, 1946 Section 1, Public Law caduceus: a, 1 946 IPatent expires October}, 1966 5 Claims. (01. 250-215? The importance atthe present-time of valves generating waves of very high frequency andadapted for coupling directly to high output circuits, such as resonantcavities and coaxial conductors, is well known. These types of valvesare designated generally under the term sealed disc valves and. theirmanufacture involves a number of problems of a mechanical nature, Inparticular, it is very important to be able to regulate with precisionthe cathode-grid space, whilst preserving strict parallelism of theelectrodes: furthermore, the width of this space, when once determined,should remain permanent. It would, moreover, be very advantageous if thecathode-grid spacing adjustment in such a valve could be effected aftersealing-off the envelope and duringactual operation of the valve, Invalves of the kind referred to, the distances between electrodes areactually of the order of a fraction of a millimetre; thus, with theusual mode of assembly, involving the sealing of electrodes into glass,it is extremely difficult to attain the requisite degree of precision,in the first instance and without subsequent adjustment;

Tothe problem of adjustingthe electrode spacing after the envelope ofthe valve has been sealed-oft various solutions have already beenproposed, and, in particular, anarrangement with a deformable plate: inuse, however, this system is generally rather precarious; moreover, ittends to increase considerably the diameter of the cathode coaxial andmakes it necessary to provide coaxial connections with external anodecircuit.

. 2 thecathode is brought to an optimum position which will be final.Thereafterthe expansible wire will remain unused.

- 2) The device may permit of varied adjust- This method, therefore,increases both the space occupied and the cost.

Thepresent invention relate to a method. of constructing sealed discvalves which method affords great facility of adjustment of the distancebetween cathode and grid after the valve has been scaled. Said methodeliminates. the dimculties enumerated above.

The process consists essentially in making the cathode movable withincertain limits, its position depending upon the length of a wireenclosed in the evacuated space and adapted to expand under the actionof heat due to the passage of an electric current. Furthermore, twoforms of embodimentv may be provided.

(1) The expansion of the wire may permit only of a single adjustment inthe course of which merits. Each time the valve is used, there will becaused to pas through, the expansible wire a steady current of adefinite value, such as to adjust the size of the cathode grid space tothe valued'esired. Thus, in each particular case, it is possible toregulate the valve to the best conditions for output,

. The invention and allthe advantages whichv it offers will be moreclearly understood by reference" to the following description which, inconjunction with'the annexed drawings, givessome non-restrictiveexamples of practical embodimerits, the features appearing from the textand from the drawings forming part of the said invention. I

Figure 1 represents a device according to, the first form of embodiment.The cathode proper I is connected to the coaxial conductor 2 by smallclips or straps 6 which are non elastic but deformable and are made of amaterial. of high electrical conductivity. A metal thrust washer 3transmits to the cathode the effort of a spiral spring] which ispre-compressed, during assembly, between said washer 3' and aninsulating washer T. The said washer 3 is retained by an expansible wire4, made of copper or nickel, for example, and fixed to it by anysuitable mechanical process; this wire first passes through a washer I,then through a drop of glass 8 which closes"- the tube 2 hermetically,and finally it emerges from said tube as at 9, The glass envelope of thevacuum tube or valve, partially represented at i0, is fused to themetallic tube 2 at a suitable zone of the latter. Under theseconditions, the interior of the tube 2 forms part of the evacuated spacewithin th envelope of the valve, The expansible wire 4' is electricallyconnected, through the washer 3, with the body of the tube 2 andconstitutes therewith a circuit, the outer terminals of which are: onthe one hand, the external portionv or extension 9 of the said -wireand, on the other hand, a conductor H welded to the exterior of 2.Between 9' and II there may be applied a potential which is finelyadjustable, for instance, by means of a ,poten tiometer device I!supplied with a potential then move the thrust washer 3 which,i 'in itsturn;

pushes up the cylindrical cathode I; The dis placement of this latter ispossible since it is held by its lateral surface by means of thedeformable straps 6. When the heating. current' is.

cut ofi, the wire 4 cools and contracts, bringing the washer 3 to itsoriginal position in which it again compresses the spring-5.. Nowvbecause the straps 6 are made of an annealed, non-elastic metal, thecathode I remains definitely located in the position to which it wasbrought when the wire 4 was expanded. This final position of l obviouslydepends upon the strength of thecurrent made to circulate in the wire4.- Since the potentiometer I2 is able to produce precise and extremelysmall variations of this current intensity, it will be understood thatthe described arrangement allows of "exerting a thrust on the cathode bycommunicating to it very small'displacements, for example, displacementsof the orderof one hundredth of a millimetre- Figure 2 represents thecomplete assembly of a triode for decimetric waves, according to theinvention; the references indicate thesame parts as on Figure 1, Therewill also be seen the heating filament l 3 in the interior of thecathode; one extremity of this filament is connected to the body of thewhole of the cathode and of the tube 2 while its other extremity isconnected to a wire l6 which passesthrough' the washer 3 in aninsulating sleeve, and then through the washer I, and terminates atalead-in connec-v tion .I'l. The connection I I thus serves as commonreturn for the filament heater current and for the current used to heatthe expansible wire 4. The triode is completed by a grid l4 and an anodeI5. I l J The arrangement is suchthat the washer 3 can shift withoutcausing the wire IE to break; for instance, this wire may be. allowed toslide in an insulating sleeve which'. serves to guide and protect it inits pas'sage throughthe' member 3. 1

One way of applying'the method of adjust ment according to the presentinvention involves the construction or triodes, for example, withcathode-grid spaces which, in the first, instance, are intentionally,oversized. The finished or partly finished valvesuare then subjected'tothe operation of a device allowing ofprecise meas-l urement of thesecathode-grid spaces. Such a measurement may, for example, be effected byan optical method if the anode is not yet. in position. The finishedtube, which has to be ad.- justed may, however be introducedinto acircuit which permits of determining its electrical characteristies-moreespecially itscoefficient of cathode is thus caused to accompany thewasher 3 in all its movements, that is to say, both outwards and inwardsrelatively to the tube 2. Consequently, if the wire 4 be heated, theexpansion of this wire will bring the cathode closer to the grid butwhen the heating is stopped said wire will contract to its initiallength, thus retracting the cathode from the grid.

This arrangement permits of continuous adjustment during the actualoperation of the triode; it is sufiicient to have available an auxiliarycurrent capable of maintaining the expansiblewire at the desiredtemperature; the

cathodeegrid space can then be increased or diminished at will until asuitable spacing is found in each case.

In addition to an easy and accurate means of adjustment, the inventionfurther presents the following advantages:

(1) The adjustment obtained is very stable, for it can be carried out atthe temperature of operation;

- '(2) The degassing of the electrodes can be .carried out with acathode-grid spacing greater amplification. The-expansiblewirel ofFigures 1 and 2 will then be heated until thecathodegrid space has beenreduced to a satisfactory value.

Figure 3 represents a cathode according to the second modification ofthe invention. The reference numerals still indicate the same elementsas in Figure 1. It will be seen that here the thrust washer 3 isimprisoned betweentwo rings 3 and I 9 integral with the cathode I. The

than that required for the normal oscillatory output. Thus, it ispossible to establish the best possible conditions for the formation ofthe cathode and a stable density of electron emission is easily obtainedover the whole of the cathodic surface.

(3) The extensible wire may be coated with an appropriate substanceenabling it to serve as a getter. Its location outside the bulb properis favourable for obtaining a good vacuum without causing trouble in theoperation of the triode.

It is to be understood that the examples above described constitute onlynon-restrictive examples and that various modifications of detail can bemade therein without departing from the scope of the invention, asclaimed hereinafter.

We claim:

1. An electron discharge tube comprising an electron emissive cathode, ametallic tube connected to said cathode by deformable metallic clips,said metallic tube being sealed through the glass envelope of saiddischarge tube and closed at its end opposite to said cathode by a cap,a thrust washer in mechanical connection with said cathode, a thermallyextensible metallic conductor having one end attached to said washer andthe other end fixed at a point in the vicinity of that end of saidmetallic tube which is opposite to said cathode, elastic means urgingthe thrust washer toward the interior of said discharge tube, andconnection means for heating the thermally extensible metallicconductor. 7 2. An electron discharge tube according to claim 1, whereinthe said thrust washer is conductive, the said thermally extensiblemetallic conductor is electrically insulated from the said metallic tubeat the end thereof opposite to said cathode, said cap closing themetallic tube consists of insulating material and has a conductor sealedtherethrough in contact with the extremity ofthe extensible metallicconductor in the vicinity of said cap.

3. An electron discharge tube according to claim 2, including a heatingfilament and wherein a second sealed-in conductor traverses the saidcap, an insulating sleeve is provided in said conductive thrust washertraversed by the extension of said second conductor, said secondconductor being connected to one end of the heating filament, andconnection from the other end of said heating filament to the cathodeitself.

4. An electron discharge tube according to claim 1, wherein the cathodeis cylindrical and of substantially the same diameter as the saidmetallic tube, and the glass envelope of said discharge tube is alsocylindrical and coaxial with said metallic tube and said cathode.

5. An electron discharge tube according to claim 1, wherein themechanical connection between the thrust washer and the cathode includesprojecting means carried by the cathode on opposite sides of the washerto cause the cathode to accompany the Washer in its opposite movements.

PIERRE CAI-IOUR. ANDRE J. VELTE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,559,714 Lilienfeld Nov. 3, 19252,208,406 Benedict July 16, 1940 2,218,886 Krause Oct. 22, 19402,424,790 Bachman et a1 July 29, 1947

